This invention relates to glazing panels and particularly to glazing panels which are intended to undergo heat treatment following application of a solar control filter.
EP 233003A describes a glazing panel carrying a sputter coated optical filter having the structure: glass substrate/SnO2 base dielectric/first metallic barrier of Al, Ti, Zn, Zr or Ta/Ag/second metallic barrier of Al, Ti, Zn, Zr or Ta/SnO2 top dielectric. The optical filter is designed to block a significant portion of the incident radiation in the infra red portion of the spectrum whilst allowing passage of a significant portion of the incident radiation in the visible portion of the spectrum. In this way, the filter acts to reduce the heating effect of incident sunlight whilst allowing good visibility through the glazing and is particularly suitable for car windscreens.
In this type of structure, the Ag layer acts to reflect incident infra red radiation; in order to fulfil this role must be maintained as silver metal rather than silver oxide and must not be significantly contaminated by adjacent layers. The dielectric layers which sandwich the Ag layer serve to reduce the reflection of the visible portion of the spectrum which the Ag layer would otherwise provoke. The second barrier serves to prevent oxidation of the Ag layer during sputtering of the overlying SnO2 dielectric layer in an oxidising atmosphere; this barrier is at least partially oxidised during this process. The main role of the fast barrier is to prevent oxidation of the silver layer during heat treatment of the coating (e.g. during bending and/or tempering) of the glazing panel by being oxidised itself rather than allowing passage of oxygen to the Ag layer. This oxidation of the barrier during heat treatment provokes an increase in TL of the glazing panel.
EP 792847A discloses a heat treatable solar control glazing panel which is based on the same principle and has the structure: glass substrate/ZnO dielectric/Zn barrier/Ag/Zn barrier/ZnO dielectric/Zn barrier/Ag/Zn barrier/ZnO dielectric. The Zn barriers positioned below each of the Ag layers are intended to be oxidised completely during heat treatment and serve to protect the Ag layers from oxidation. As well known in the art, the structure of having two, spaced Ag layers rather than a single Ag layer increases the selectivity of the filter.
EP 275474 A discloses a heat treatable solar control panel having the structure: glass substrate/zinc stannate dielectric/Ti barrier/Ag/Ti barrier/zinc stannate dielectric. Ti barriers are generally favoured in this type of heat treatable structure due to their high affinity for oxygen and relative ease with which they can be oxidised to form titanium oxide.
According to one aspect, the present invention provides a glazing panel as defined in claim 1.
The coating layers are preferably deposited by sputtering, preferably magnetron sputtering but other deposition techniques may be used. Different layers of the coating stack may be deposited using different techniques.
The upper layers in the base and central antireflective layers may have the same or substantially the same composition. This may facilitate the use of substantially similar targets to deposit these layers and/or substantially similar deposition conditions.
The combination of the defined upper layers in the base and central antireflective layers as part of the defined coating stack may facilitate the production of glazing panels (and particularly of laminated windscreens) having TL greater than 75% once subjected to heat treatment whilst still providing an advantageous combination of repeatable thermal stability during heat. treatment, low haze, mechanical and chemical resistance and desired colour in reflection and/or transmission.
One or preferably both of the additional materials X and Y is preferably Sn and/or Al. This may give a particularly advantageous combination of properties.
The proportion of Zn in the mixed oxide that forms the base antireflective upper layer and/or that which forms the central antireflective upper layer may be such that ratio X/Zn and/or the ratio Y/Zn is between about 0.03 and 0.3 by weight.
Arranging one or each of the upper layers of the base and/or central antireflective layers in direct contact with its overlying infra-red reflecting layer may also facilitate achieving high levels of TL during heat treatment. Alternatively, an addition layer, for example, a barrier layer, may be interposed between one or each of the upper layers of the base and central antireflective layers and its overlying infra red reflecting layer. Such an additional barrier may be a layer comprising Ti and/or comprising an oxide of Ti. The additional barrier layer may have a geometrical thickness of between about 5 xc3x85 and 60 xc3x85.
The base antireflective upper layer and/or the central antireflective upper layer may have a geometrical thickness of less than about 200 xc3x85, less than about 150 xc3x85, less than about 130 xc3x85 or less than about 110 xc3x85. This may provide advantageous mechanical properties to the coating stack, particularly with respect to resistance to peel tests.
The base antireflective upper layer and/or the central antireflective upper layer may have a geometrical thickness of greater than about 30 xc3x85, greater than about 50 xc3x85 greater than about 100 xc3x85. This may provide a sufficient thickness to enhance the properties of the coating stack, particularly with respect to TL obtainable after heat treatment.
The central antireflective lower layer may comprises at least one layer which provides a sufficient block to the migration of oxygen and/or sodium and/or other materials to prevent significant contamination of and/or diffusion of the layers of the coating stack. Preferably, the central antireflective lower layer is in direct contact with the first barrier layer and comprises a material which resists diffusion of the first barrier layer during heat treatment. The combination of a central antireflective lower layer as defined in claim 5 with a first barrier which is deposited at least partially in metallic or substantially metallic form and subsequently oxidised during heat treatment (and particularly a barrier that comprises or consists essentially of metallic Ti when deposited) may permit particularly high thermal stability of the coating stack during heat treatment. It is believed that diffusion of material from the first barrier layer into the central antireflective lower layer during heat treatment and particularly during severe heat treatment may, in some coating stack arrangements be a critical factor in determining thermal stability of the coating stack; the composition of central antireflective lower layer defined in claim 5 may significantly mitigate against such diffusion.
The base antireflective lower layer may comprise at least one layer which provides a sufficient block to the migration of oxygen and/or sodium and/or other materials to prevent significant contamination of and/or diffusion of the layers of the coating stack. The use of a base antireflective lower layer as defined in claim 6 may be used to facilitate this whilst, in addition, facilitating the arrangement and control of the deposition conditions.
The use of a top antireflective layer as defined in claim 9 may facilitate the arrangement and control of the deposition conditions for the overall coating stack. In addition, this layer may be arranged to provide a block to migration of oxygen during heat treatment and/or diffusion of the second barrier layer.
The top antireflective layer may comprise at least one layer which comprises a mixed oxide of Zn and at least one additional material W, in which the ratio W/Zn in that layer is between 0.02 and 0.5 by weight and in which W is one or more of the materials selected from the group comprising Sn, Al, Ga, In, Zr, Sb, Bi, Mg, Nb, Ta and Ti. This may improve the thermal stability of the coating stack during heat treatment and/or its mechanical or chemical resistance, particularly when used as defined in claim 10.
According to further aspects, the invention provides a glazing panel as defined in claim 13 and for use of a glazing panel as defined in claim 14.
According to another aspect, the invention provides a method as defined in claim 15.
The invention may provide an advantageous combination of properties for the glazing, for example:
particularly good levels of TL following heat treatment
particularly good thermal stability during heating of the glazing panel, for example during tempering and/or bending. This may facilitate bending of coated glazing panels, particularly to produce complex shapes, without provoking unacceptable variations in colour over the surface of the glazing panel. Colour variations during heat treatment may be caused by lack of thermal stability of the coating stack when subjected to conditions necessary to bend and/or temper the glass substrate. This aspect may be particularly enhanced by the use of a central antireflective lower layer as defined in claim 5 to inhibit significant diffusion of the first barrier layer;
ease and controllability of deposition: the antireflective layers according to the present invention may be deposited more easily and with more control than, for example, Al203 or SiO2. Whilst Al203 and SiO2 show a good degree of thermal stability they are difficult to deposit using common sputtering techniques.
good mechanical resistance: the antireflective layers according to the present invention may be used without prejudicing the mechanical resistance of the coating. In particular, they may perform well in pummel tests when the glazing panel is used in a laminated structure.
compatibility with Ag: crystallisation of the Ag layer affects its optical properties. A pure ZnO layer adjacent the Ag can lead to excessive crystallisation of the Ag and to problems of haze in the coating, particularly during heat treatment. However, where an antireflective layer does not consist of ZnO there may be insufficient recrystallisation of the Ag layers resulting in a level of infra red reflection and a level of electrical conductivity in the coating which are below the optimum obtainable. The present invention may be used to favour crystallisation to a sufficient degree to provide good infra red reflecting properties whilst avoiding excessive haze. In particular, it may provide a favourable crystallisation compared with an antireflective layer composed of TiO2 or SnO2. One possible explanation for this may be that the presence of the additional material X or Y in the zinc oxide structure may reduce the crystal grain growth in the mixed oxide layer, especially perpendicular to the substrate. This may result in a less crystalline, more amorphous structure which reduces diffusion that might otherwise be likely to occur at crystal grain boundaries.
production cycle time: an oxide layer which is a mixture of Zn and at least one of the specified addition materials may have a higher refractive index than antireflective layers of, for example, ZnO and SnO2, which are commonly used in similar structures and yet will be quicker to deposit than known antireflective layers having relatively high refractive indexes, for example, TiO2. Consequently, this may enable the production cycle time to be improved.
good selectivity: the higher refractive Index may, in addition, facilitate an increase in the selectivity of the coating stack.
low emissivity, notably an emissivity of less than 0.35, preferably less than 0.32 or less than 0.30, particularly after heat treatment
low electrical resistance, notably a resistance per square of less than 3 ohms per square, preferably less than 2.8, 2.5 or 2.3 ohms per square, particularly after heat treatment
Particularly advantageous properties may be obtained if additional material X or Y consists
essentially of Sn
of Sn with one or more additional materials from the specified group of materials, for example, Ti and Al
essentially of Al
of Al with one or more additional materials from the specified group of materials.
The present invention may be particularly advantageous in facilitating manufacture of laminated windscreens or other glazings having colour co-ordinates on the CIElab scale of L*=40xc2x12.5 a*=xe2x88x926xc2x12.5 b*=xe2x88x922xc2x12.5. Whilst known coating stacks may enable such windscreens to be manufactured, particularly for simple models which do not require severe heating conditions to provide desired configurations once bent, the present invention, by providing a coating stack which is particularly stable during heat treatment of the glazing panel may allow more complex bent forms to be produced, and/or may provide significantly better industrial yield with less rejects and/or may enable the use of less sophisticated bending methods and/or may ensure that such characteristics may be consistently obtained for industrially produced glazings whilst still providing a TL of at least 75%, and indeed a TL which may be of or above 76%.
Similarly, the present invention may facilitate manufacture of laminated windscreens or other glazings in which the variation of colour xcex94E* over the surface of the glazing is less than 2, preferably less than 1.5 or 1.2 and more preferably less than 1 where the variation of colour xcex94E* is calculated as:
xcex94E*=(L*2+a*2+b*2) where L* a* and b* are measured on the CIElab scale.
The variation in colour over the surface of a windscreen will depend on the complexity of the windscreen, the heating method and conditions used to bend the glazing panel and the thermal stability of the coating stack to such colour variations. Whilst prior known coating stacks may enable such low levels of colour variation to be achieved particularly for simple windscreens or under certain heating conditions or with certain levels of rejection for non-conformity, the present invention may be used to facilitate industrial manufacture of such windscreens under significantly more advantageous industrial conditions.
The term xe2x80x9cheat treatable glazing panelxe2x80x9d as used herein means that the glazing panel carrying the coating stack is adapted to undergo a bending and/or thermal tempering and/or thermal hardening operation without the haze of the so treated glazing panel exceeding 0.5, and preferably without the haze exceeding 0.3. The term xe2x80x9csubstantially haze free heat treated glazing panelxe2x80x9d as used herein means a glazing panel which has been bent and/or thermally tempered and/or thermally hardened and has a haze that does not exceed 0.5 and which preferably does not exceed 0.3. The invention may be particularly advantageous in facilitating manufacture in which a coating stack is deposited on a substantially flat or planar glass substrate to produce a glazing panel which may be subsequently heat treated, for example bent or tempered.
The filter stack may comprise one or more barrier layers underlying and/or overlying the infra red reflecting layer, as is known in the art. Barriers of, for example, one or more of the following material may be used: Ti, Zn, Cr, xe2x80x9cstainless steelxe2x80x9d, Zr, Ni, NiCr, ZnTi NiTi and ZnAl. Such barriers may be deposited, for example, as metallic layers or as sub-oxides (i.e. partially oxidised layers). Alternatively, nitrided barrier layers may also be used. The barrier layers in such coating stacks may serve to protect the infra red reflecting layers from unacceptable levels of degradation during the deposition of overlying layers and/or during heat treatment of the coating stack.
One or more of such barrier layers may comprise the same materials as the mixed oxide layer, particularly the adjacent mixed oxide layer. This may facilitate management of targets and control of deposition conditions and in the latter case may provide good adhesion between the layers and thus good mechanical durability of the coating stack.
Heat treatment may provoke an increase in the TL of the glazing panel. Such an increase in TL may be advantageous in ensuring that TL is sufficiently high for the glazing panel to be used in a vehicle windscreen. TL may increase in absolute terms during heat treatment by, for example, greater than about 2.5%, greater than about 3%, greater than about 5% , greater than about 8% or greater than about 10%.